Diverse Activities of Carotenoid Cleavage Oxygenases - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 389

19 Diverse Activities of

Carotenoid Cleavage
Oxygenases

Erin K. Marasco and Claudia Schmidt-Dannert

CONTENTS
19.1 Introduction to Apocarotenoids ............................................................................................389
19.2 Apocarotenoid Formation..................................................................................................... 390
19.3 Carotenoid Cleavage Oxygenases......................................................................................... 392
19.3.1 Plant CCOs................................................................................................................ 395
19.3.1.1 NCEDS ....................................................................................................... 395
19.3.1.2 CCDS .......................................................................................................... 397
19.3.1.3 ZCD and LCD ............................................................................................ 398
19.3.2 Vertebrate CCOs ....................................................................................................... 398
19.3.3 Fungal CCOs.............................................................................................................399
19.3.4 Cyanobacterial CCOs................................................................................................400
19.3.5 Bacterial CCOs ......................................................................................................... 401
19.4 Structure and Mechanism of CCOs......................................................................................402
19.5 Biological Functions of Apocarotenoids ..............................................................................404
19.6 Commercial Relevance of Apocarotenoids ..........................................................................408
19.6.1 Apocarotenoid Biosynthesis in Recombinant Hosts .................................................408
19.6.2 Improving CCO In Vitro Activity .............................................................................409
19.7 Conclusions and Outlook ...................................................................................................... 410
References ...................................................................................................................................... 410

19.1 INTRODUCTION TO APOCAROTENOIDS
Apocarotenoids are isoprenoid compounds that contain shortened carbon backbones compared to
the naturally occurring carotenoids from which they are derived by oxidative cleavage. Cleavage
of the carotenoid backbone can occur through nonspecii c nonenzymatic (e.g., radical formation)
or enzymatic oxidation (e.g., peroxidases). However, in biological systems where apocarotenoids
exhibit specii c biological activities, the oxidative cleavage of the carotenoid backbone is catalyzed
by a class of enzymes known as carotenoid cleavage enzymes. Unlike unspecii c carotenoid cleav-
age, these enzymes catalyze cleavage of specii c double bonds of the carotenoid backbone. Enzymes
with preferences for different carotenoid substrates and activities for cleaving different sites within
a specii c carotenoid have been identii ed and are discussed in detail in this chapter. Because the
mechanism by which these enzymes catalyze oxidative cleavage, either via a monooxygenase or
dioxygenase mechanism, is currently controversial, we use the term carotenoid cleavage oxygenases
(CCOs).

389